No 10 insisted Chancellor Gordon Brown was saying nothing new last night when he sparked controversy by confirming he wanted to retain an independent nuclear deterrent "for the long term".

Speaking at the Lord Mayor's annual banquet in the Mansion House, the Chancellor said that the Government would show "strength of national purpose" in "protecting our security in this Parliament and the long-term - strong in defence in fighting terrorism, upholding Nato, supporting our Armed Forces at home and abroad, and retaining our independent nuclear deterrent."

Prime Minister Tony Blair's official spokesman said Mr Blair had also voiced his support for the nuclear deterrent in interviews during the last election campaign.

A commitment to retain the deterrent was also included in Labour's 2005 election manifesto.

Mr Blair's official spokesman said today: "Decisions will be taken in due course and there will be a proper debate.

"The issue of the replacement of Trident is one that the Government will address in this parliament.

"It is undoubtedly a difficult issue, it will undoubtedly lead to proper debate and proper discussions.

"But the Prime Minister believes we have to face up to these decisions in the interests of the country."

The spokesman said a White Paper - a document setting out the Government's intentions - would be published.

He added: "The key point is there will be a proper discussion and a proper debate. the Government will set out its reasons for a decision, whatever it is."

"What he said is entirely consistent with what is in the manifesto and it's entirely consistent with what the Prime Minister has said," he told BBC Radio 4's Today programme.

He said it was "too early to decide" whether MPs would be allowed a vote on the issue.

"This will in part depend on what decisions we actually take in the future but there will be full transparency about this.

"The fact that the Chancellor is speaking about it in the context of a range of other policy issues is an indication of how transparent we are about this.

"We've promised the fullest possible Parliamentary debate on this when the time is right and that's exactly what will happen," he added.

Shadow defence secretary Liam Fox said of the Chancellor's remarks: "This is just more spin designed to cast Gordon Brown as a statesman.

"The Chancellor is reheating an old pledge to retain the current nuclear deterrent, but he is not committing to replacing the independent nuclear deterrent when it reaches the end of its current life."

Meanwhile, leading Labour left-winger Alan Simpson denounced Mr Brown's comments as "a pre-emptive strike on parliamentary democracy", telling the BBC it was "bizarre" that the Chancellor should effectively announce his intentions to the City before MPs had a chance to discuss the matter in the Commons.

And Liberal Democrat defence spokesman Nick Harvey said: "Gordon Brown's posturing on Trident is smothering the national debate that this Government promised to the British people.

"The British people deserve a comprehensive White Paper and full parliamentary scrutiny of a scheme that may cost up to £25 billion to replace."